In order to achieve efficient combustion in a combustion chamber even at low temperatures, and to avoid the emission of high amounts of nitric oxides, it has been suggested that the combustion be performed in the presence of a catalyst. By using a catalyst it is thus possible to achieve almost complete combustion of fuel/air-mixtures in which the percentage of fuel is very low. In this way, operation of the catalytic combustion chamber can be very safe, since the gas mixture which is used is not inflammable at atmospheric pressure in the absence of a catalyst. Accordingly, there is no risk of explosion if the air/fuel mixture should leak out of the catalytic combustion chamber. In addition, a catalytic combustion chamber is reliable, and does not generate irritating noise when in operation.
In Japanese Patent Application No. 2-197245 a catalytic combustion chamber is described comprising two catalytic reactors, wherein a main catalytic reactor is heated by the exhaust gases from a preheating catalytic reactor. The preheating catalytic reactor is heated to its ignition temperature by means of an electrically heated heater. A portion of the heat generated by combustion in the preheating catalytic reactor is utilized for heating a carburetor in order to vaporize the fuel. An ignition process of this type is comparatively slow, and requires a large initial consumption of electricity. It also results in high emissions of carbohydrates and carbon monoxide.
A further catalytic combustion chamber comprising two serially coupled catalytic reactors is described in Japanese Patent Application No. 60-27994. This publication also utilizes a two-step process for initiating catalytic combustion. Instead of heating the first catalytic reactor when igniting the catalytic combustion chamber, the gas which is conducted through the catalytic reactor is heated, thereby accomplishing ignition. An ignition process of this type demands a high initial energy supply and, consequently, involves a large energy consumption during the ignition process.
These previously known two-step ignition processes do not significantly diminish either the emissions of incompletely combusted fuel or the consumption of electricity during the ignition process. For this reason, there remains considerable demand for a simple, quick and electricity saving ignition process for a catalytic combustion chamber having low emission of carbohydrates and carbon monoxide.